Measurement of body water by multifrequency bioelectrical impedance spectroscopy in a multiethnic pediatric population.

BACKGROUND: Bioelectrical impedance spectroscopy (BIS) may provide a noninvasive, rapid method for the assessment of total body water (TBW), extracellular water (ECW), and intracellular water (ICW). Few studies, however, have examined the accuracy of BIS in pediatric populations. OBJECTIVE: Our objective was to evaluate the accuracy of BIS for the measurement of TBW, ECW, and ICW in healthy children. DESIGN: Dual-energy X-ray absorptiometry (DXA), total body potassium (TBK), and BIS measurements were performed in 347 children (202 males and 145 females aged 4-18 y). The reference values for TBW, ECW, and ICW were defined by using a DXA+TBK model. BIS values were evaluated by using the method of Bland and Altman. A randomly selected calibration group (n = 231) was used to derive new BIS constants that were tested in the remaining group (n = 116). RESULTS: BIS values were highly correlated with the reference values (r(2) = 0.94-0.97, P < 0.0001), but differences between the BIS and DXA+TBK models for individuals were significant (P < 0.001). Use of new BIS constants reduced the mean differences between the BIS and DXA+TBK models; the SDs of the mean differences were improved (1.8 L for TBW, 1.4 L for ICW, and 1.0 L for ECW) for the total population. CONCLUSIONS: On a population basis, BIS can be calibrated to replace the DXA+TBK model for the assessment of TBW, ECW, and ICW in healthy children. The accuracy of the BIS measurement in individual children may be refined further by using age- and sex-specific adjustments for the BIS calibration constants.     

Assessment of body composition in 8-11 year old children by bioelectrical impedance

In 64 prepubescent schoolchildren, 33 boys and 31 girls, aged 8-11 years, body composition was measured by means of anthropometry, densitometry and bioelectrical impedance. From body density the body fat percentage was calculated using age-specific density values for the fat-free mass. Boys and girls younger than 10 years did not differ in body composition. Older boys however had higher body weights, higher body densities and lower body impedance values. Fat-free mass as determined by densitometry could be predicted by body impedance and body weight with a prediction error of 1.31 kg. The prediction formula was sex-specific. Omitting the impedance in the prediction equation resulted in a 7 per cent lower explained variance and an only slightly higher prediction error of the FFM of 1.65 kg. The prediction formulas from the literature, developed in adult populations, grossly overestimated the fat-free mass in children, probably due to a different water distribution between the intra- and extra-cellular spaces.     

Assessment of body composition by bioelectrical impedance in children and young adults is strongly age-dependent

Body composition was measured in a group of 246 children and young adults, ranging in age from 7 to 25 years, by means of densitometry, body impedance (R) and anthropometry. Body fat percentage and fat-free mass (FFM) were calculated from body density using age-specific calculation formulas. From body impedance, FFM and body height, the specific impedance of the body (rho = R*FFM/height) was calculated in which body impedance is corrected for differences in the shape of the conductor. From age 10 onwards the specific impedance was positively related with age until age 13 in girls and age 16 in boys, after which it stabilized in boys at a significantly higher level than in girls. Based on the relationship of the specific impedance with age and sex, three age groups could be defined in which the relation between FFM and body impedance was analysed: age group I, boys and girls younger than 10 years; age group II, boys aged 10-15 years, girls aged 10-12 years; age group III, boys 16 years and older, girls 13 years and older. The regression equation in age group I had the same slope as the sex-specific regression equations in age group III. The regression equation in age group II had a steeper slope compared to the regression equations in age group I and III. Thus the relationship between FFM and body impedance was found to be slightly S-shaped, being identical for boys and girls until age 13, after which sex differences became apparent. For the different age categories the best prediction formula for the FFM from body impedance, sex, age and anthropometric variables was calculated. The prediction error of the age-specific regression equations was lower than the prediction error of the regression equation for the entire population.     

Comparison of body composition measurement with whole body multifrequency bioelectrical impedance and air displacement plethysmography in healthy middle-aged women

Our purpose was to evaluate accuracy of multifrequency bioelectrical impedance analysis (MFBIA) using air displacement plethysmography (ADP) as the criterion measure. Body composition of 27 women was assessed by ADP followed immediately by MFBIA. There was a strong relationship (p = .01) between ADP and MFBIA in absolute lean mass (r = 0.80), absolute fat mass (r = 0.99), percent lean mass (r = 0.91), and percent fat mass (r = 0.91). Although MFBIA consistently overestimated lean mass and underestimated fat mass compared with ADP, agreement between measurements was within 2%-3% body fat. An accurate assessment tool, MFBIA can be useful in clinical settings.     

Assessment of intracellular water by whole body bioelectrical impedance and total body potassium in HIV-positive patients

OBJECTIVE: Bioelectrical impedance analysis (BIA) is widely used as bedside assessment of body composition. Body cell mass (BCM) and intracellular water (ICW) are clinically important body compartments. Estimates of ICW obtained from BIA by different calculation approaches were compared to a reference method in male HIV-infected patients. PATIENTS: Representative subsample of clinically stable HIV-infected outpatients, consisting of 42 men with a body mass index of 22.4 +/- 3.8 kg/m(2)(range, 13-l31 kg/m(2)). METHODS: Total body potassium was assessed in a whole body counter, and compared to 50 kHz monofrequency BIA and multifrequency bioelectrical impedance spectroscopy. Six different prediction equations for ICW from BIA data were applied. Methods were compared by the Bland-Altman method. RESULTS: BIA-derived ICW estimates explained 58% to 73% of the observed variance in ICW (TBK), but limits of confidence were wide (-16.6 to +18.2% for the best method). BIA overestimated low ICW (TBK) and underestimated high ICW (TBK) when normalized for weight or height. Mono- and multifrequency BIA were not different in precision but population-specific equations tended to narrower confidence limits. CONCLUSION: BIA is an unreliable method to estimate ICW in this population, in contrast to the better established estimation of total body water and extracellular water. Potassium depletion in severe malnutrition may contribute to this finding but a major part of the residual between methods remains unexplained.     

Evaluation of partial body composition using bioelectrical impedance in Japanese children

To clarify the growth pattern of body composition by body part for the management of childhood obesity, we measured body fat and muscle using BIA (bioelectrical impedance analysis) in 685 Japanese elementary schoolchildren (aged 6-11 years). The growth patterns of percentage body fat (%BF), fat mass (FM), and muscle mass (MM) were examined throughout the whole body and in various body parts. The %BF of the whole body was greater in females than in males, and this difference widened with age. The %BF, FM, and MM in each body part showed similar growth patterns and gender differences to those of the whole body. The mean %BF of the left limbs was higher than that of the right limbs at all age groups. BMI was strongly correlated with %BF in both sexes. In conclusion, the compositions of all body parts change similarly with age, and gender differences are also similar in childhood. The effect of one's dominant arm on body composition is seen at a young age. The accumulation of body composition data according to body part is indispensable for understanding childhood body composition and managing obesity.     

Changes in body fluid compartments estimated by multifrequency bioelectric impedance analysis in patients treated by hemodialysis]

Bioimpedance is a simple non-invasive method of assessing body composition. The aim of this study was to investigate the effect of changes in body fluid related to haemodialysis on measured bioimpedance parameters, to determine correlation between bioimpedance data and the volume of ultrafiltratum, and to collect data on alterations of body fluids resulting from a treatment. Measurements were done on 19 patients (mean age 36.7 years) prior to and after haemodialysis. After dialysis we found significantly higher impedance values on each measured frequency (1, 5, 10, 50, 100 kHz) (p < 0.001). An inverse correlation was found between the changes in body weight (x) and resistance at 50 kHz (y): y = 8.4830-2.1850x (r = 0.7167, p < 0.01). Total body water calculated by bioimpedance analysis (BIA) decreased from 38.47 +/- 8.567 litres (56.07%) to 35.06 +/- 8.045 significantly (p < 0.001), and the reduction of extracellular water proved to be also significant [from 15.76 +/- 2.992 litres (22.97%) to 14.06 +/- 2.736 litres (21.17%), p < 0.001]. The relationship between the change in calculated body water (x) and the volume of ultrafiltratum (y) is: y = -0.5590 + 0.5864x (r = 0.4898 p < 0.05), bioimpedance in our study overestimated the fluid loss by 55%. The intradialytical shifts between extra- and intracellular spaces might be responsible for the difference in the two values.     

Errors in estimating peritoneal fluid by bioelectrical impedance analysis and total body electrical conductivity.

Whole-body bioelectrical impedance analysis (BIA) and total body electrical conductivity (TOBEC) have been used to estimate body composition and generalized changes in total body water (TBW). The sensitivity of these methods to measure small, rapid, localized changes in body water has not been fully evaluated. We compared the prediction of TBW by whole-body and segmental BIA and TOBEC with deuterium oxide dilution (D2O) in 10 control subjects and 7 renal failure patients receiving continuous ambulatory peritoneal dialysis (CAPD) prior to and after dialysate infusion. Using D2O as the reference method, there was no significant mean residual error between TBW predicted by BIA and TOBEC in controls (?1.2 +/? 1.5 and ?0.9 +/? 1.0 kg) and CAPD patients pre-infusion (?1.0 +/? 2.0 and 0.29 +/? 2.01 kg). After infusing 1.9 +/? 0.18 kg dialysate, the mean residual error between change in body weight and the three methods was ?0.44 +/? 0.53 kg for D2O (p < 0.1), ?1.7 +/? 0.25 kg for BIA (p < 0.0001), and 1.2 +/? 0.4 kg for TOBEC (p < 0.001). Segmental BIA detected a 7.6% reduction in trunkal resistance with no significant change across the limbs, consistent with abdominal fluid accumulation. It is concluded that whole-body BIA underpredicts and TOBEC overpredicts small changes in peritoneal fluids.     

Assessment of body composition by bioelectrical impedance in a population aged greater than 60 y

Body composition was measured in a group of 35 healthy men and 37 healthy women aged 60-83 y. Body mass index (BMI) in men was 25.0 +/- 2.2 kg/m2 (means +/- SD) and in women, 25.9 +/- 3.2 kg/m2. BMI was low in relation to body fat percentage as determined by skinfold-thickness measurements or densitometry in comparison with the relation found in younger adults. Mean body fat percentage of the male subjects (aged 70.4 +/- 5.2 y) as determined by densitometry was 31.0 +/- 4.5%, whereas in women (aged 68.0 +/- 5.2 y) it was 43.9 +/- 4.3%. Body impedance correlated with fat-free mass (FFM). The best prediction formulas for the FFM from body impedance and anthropometric variables were 1) FFM (kg) = (0.671 x 10(4) x H2/R) + 3.1S + 3.9 where H is body height (m), R is resistance (omega), and S is gender (females, 0; males, 1) (r = 0.94; SEE = 3.1 kg) and 2) FFM (kg) = (0.360 x 10(4) x H2/R) + 0.359BW + 4.5S - 20T + 7.0 where BW is body weight (kg) and T is thigh circumference (m) (r = 0.96; SEE = 2.5 kg). The prediction equations from the literature, generally determined in younger populations, overestimated FFM in elderly subjects by approximately 6 kg and are not applicable to elderly subjects.     

Assessment of fat-free mass using bioelectrical impedance measurements of the human body

A method which involves the measurement of bioelectrical resistive impedance (R) for the estimation of human body composition is described. This method is based upon the principle that the electrical conductivity of the fat-free tissue mass (FFM) is far greater than that of fat. Determinations of R were made in 37 healthy men aged 28.8 +/- 7.1 yr (mean +/- SD) using an electrical impedance plethysmograph with a four electrode arrangement that introduces a painless signal (800 microA at 50 kHz) into the body. FFM was assessed by hydrodensitometry and ranged from 44.6-98.1 kg. Total body water (TBW) determined by D2O dilution and total body potassium (TBK) from whole body counting were 50.6 +/- 10.3 L and 167.5 +/- 38.1 g, respectively. Test-retest correlation coefficient was 0.99 for a single R measurement and the reliability coefficient for a single R measurement over 5 days was 0.99. Linear relationships were found between R values and FFM (r = -0.86), TBW (r = -0.86), and TBK (r = -0.79). Significant (p less than 0.01) increases in the correlation coefficients were observed when the predictor Ht2/R was regressed against FFM (r = 0.98), TBW (r = 0.95), AND TBK (r = 0.96). These data indicate that the bioelectrical impedance technique is a reliable and valid approach for the estimation of human body composition. This method is safe, noninvasive, provides rapid measurements, requires little operator skill and subject cooperation, and is portable. Further validation of this method is recommended in subjects with abnormal body composition.     

Estimation of body composition by bioelectrical impedance in cancer patients

Measurement of body composition is important in the assessment of nutritional status in cancer patients. The purpose of this study was to validate the bioelectrical impedance (BI) method for body composition estimation in 33 elderly cancer patients (mean age 66 +/- 9 years) using the deuterium dilution technique (2H2O) as the reference method. Height2/Resistance (H2/R) correlated significantly with total body water (TBW) computed from 2H2O (r = 0.89, P less than 0.001; s.e.e. = 2.4 l). The prediction equation for TBW improved significantly (P less than 0.001) by addition of H2/R to the predictor variables weight, height, age and sex. We conclude that BI is a useful measure for the assessment of body composition in cancer patients.     

Estimation of total body water by bioelectrical impedance analysis

Total body water (TBW) measured by bioelectrical impedance analysis (BIA) was directly compared with deuterium-isotope dilution in a total of 58 subjects. First, sex-specific and group equations were developed by multiple regression analysis in (10 each) obese and nonobese men and women. Height/resistive impedance was the most significant variable used to predict deuterium-dilution space (D2O-TBW) and, combined with weight, yielded R = 0.99 and SE of estimate = 1.75 L. Equations predicted D2O-TBW equally well for obese and nonobese subjects. Second, the equations were prospectively tested in a heterogeneous group of 6 males and 12 females. Sex-specific equations predicted D2O-TBW with good correlation coefficients (0.96 and 0.93), total error (2.34 and 2.89 L), and a small difference between mean predicted and measured D2O-TBW (-1.4 +/- 2.05 and -0.48 +/- 2.83 L). BIA predicts D2O-TBW more accurately than weight, height, and/or age. A larger population is required to validate the applicability of our equations.     

The Stayhealthy bioelectrical impedance analyzer predicts body fat in children and adults

Bioelectrical impedance analysis (BIA) is a time-efficient and cost-effective method for estimating body composition. We hypothesized that there would be no significant difference between the Stayhealthy BC1 BIA and the selected reference methods when determining body composition. Thus, the purpose of the present study was to determine the validity of estimating percent body fat (%BF) using the Stayhealthy BIA with its most recently updated algorithms compared to the reference methods of dual-energy x-ray absorptiometry for adults and hydrostatic weighing for children. We measured %BF in 245 adults aged 18 to 80 years and 115 children aged 10 to 17 years. Body fat by BIA was determined using a single 50 kHz frequency handheld impedance device and proprietary software. Agreement between BIA and reference methods was assessed by Bland and Altman plots. Bland and Altman analysis for men, women, and children revealed good agreement between the reference methods and BIA. There was no significant difference by t tests between mean %BF by BIA for men, women, or children when compared to the respective reference method. Significant correlation values between BIA, and reference methods for all men, women, and children were 0.85, 0.88, and 0.79, respectively. Reliability (test-retest) was assessed by intraclass correlation coefficient and coefficient of variation. Intraclass correlation coefficient values were greater than 0.99 (P < .001) for men, women, and children with coefficient of variation values 3.3%, 1.8%, and 1.7%, respectively. The Stayhealthy BIA device demonstrated good agreement between reference methods using Bland and Altman analyses.     

Assessment of body composition by bioelectrical impedance analysis without the need for measurement of height

Conventional whole-body single frequency bioelectrical impedance analysis (BIA) of body composition typically uses height as a surrogate measure of conductor length. A new method of BIA analysis for the prediction of body cell mass (BCM) and extracellular water (ECW, as % body weight) not using height has been introduced-the Soft Tissue Analyser (STA(TM), Akern Sri, Florence, Italy)-making it ideal for use in subjects where measurement of height is difficult or impossible. The performance of the new analytical method in predicting BCM and ECW in 139 normal control subjects was assessed by comparison with reference data obtained from a four-component (4-C) model of body composition and with predictions obtained from conventional BIA analysis. Both predicted BCM and ECW were strongly (r=0.82, SEE=6.3 kg and 0.89, SEE=1.3 kg respectively) correlated with the corresponding 4-C model measurements although differing significantly from the lines of identity (P<0.0001). Fat-free mass, calculated from STA estimates of BCM and ECW, was better predicted (r=0.91, SEE=5.6 kg). The significant differences in STA-group mean values for BCM and ECW and wide limits of agreement compared with the reference data indicate that the method cannot be used with confidence for prediction of these body compartments despite the obvious advantage of not requiring an accurate measurement of height.